By some recent estimates there are over 1 billion passenger vehicles in the world, with over a quarter of that number in the United States alone. The tires on the wheels of these vehicles are, for a variety of reasons, chronically underinflated. This underinflated condition increases carbon emissions while reducing fuel economy, tire life, and braking and steering performance, yet often goes uncorrected for extended periods of time due to the required effort and low priority associated with re-inflating the tires to proper levels.
Various efforts have been made to address this issue. Among the less successful efforts are various tire and wheel designs incorporating automatic inflation systems. It appears that these efforts have been unsuccessful for a number of reasons including: the cost of such systems, design flaws, and requirements for substantial modifications to the existing tire and wheel designs. It is believed that these issues are obstacles to retrofitting existing vehicle wheels, dooming most of these efforts to failure.
The most successful of these efforts is the incorporation of wireless pressure sensors in tire valve stems to detect underinflated conditions and to alert the driver of the need for such prompt action. Yet even this effort has met with limited success as drivers often postpone such action until it is convenient.